1. Field of the Invention
The present invention relates to systems for actuating one or more tools adapted for use in a wellbore.
2. Description of the Related Art
Hydrocarbons such as oil and gas are recovered from a subterranean formation using a wellbore drilled into the formation. A number of tools are used throughout the process of drilling and completing the wellbore and also during the production life of the well. Many of these tools are energized using pressurized fluid that is self-contained in the tool, pumped downhole from the surface, or fluid that is produced from the well itself. These tools, which are sometimes referred to as hydraulically actuated tools, can be put to a number of uses.
One use for hydraulically actuated tools is to set a liner hanger. During drilling, the wellbore is lined with a string of casing that is cemented in place to provide hydraulic isolation and wellbore integrity. Commonly, multiple strings of casing are set in a well in a successive fashion. For example, a first string of casing is set in the wellbore after the well is drilled to a first depth and a second string of casing is run into the wellbore after the well is drilled to a second depth. The second string is set such that the upper portion of the second string of casing overlaps with the lower portion of the first string of casing. Any string of casing that does not extend back to the surface is generally referred to as a liner. The second string is then cemented into the wellbore as well. This process may be repeated as needed.
The liner hanger is used to hang or anchor a liner off of a string of other casing string. Several types of liner hangers are known in the art, which includes hydraulic liner hangers. In conventional hydraulic liner hangers, fluid is supplied under pressure into an annular space between a mandrel and a surrounding cylinder. The hydrostatic pressure of the fluid between the cylinder and the mandrel creates a force on the inner surface area of the cylinder that causes the cylinder to slide longitudinally.
Conventionally, the hydraulic liner hanger is set by applying a predetermined level of hydrostatic pressure to the liner hanger. That is, the liner hanger is run into the wellbore while in contact with a fluid having a first hydrostatic pressure and then actuated by increasing the pressure in the fluid. In an conventional arrangement, a ball is dropped into the wellbore and landed on a seat that is positioned generally downhole of the liner hanger. Fluid is then injected into the wellbore under pressure in order to actuate the hydraulic liner hanger.
Conventional hydraulic liner hangers can prematurely set if there is a pressure spike of sufficient magnitude in the drill string or if the pressure of the fluid external to the liner hanger unexpected drops. Conventional measures to prevent unintended setting of the liner hanger include the use of shear pins to mechanically restrain the cylinder while the liner assembly is run into the hole and closures or flow restriction devices that prevent fluid from entering the hydraulic liner hanger until the liner hanger is ready to be set.
These conventional measures have various drawbacks that include, but are not limited to, expense and tool complexity. These conventional measures may also impose undesirable constraints in deployment of the liner hanger such as permissible bounds for drilling fluid circulation pressures and flow rates. Moreover, the drawbacks of conventional hydraulic liner hanger are merely illustrative of the general drawbacks of wellbore tools in general that operate using hydrostatic pressure while in the wellbore.
The present invention addresses these and other drawbacks of the prior art.